Thesis (MSc)--Stellenbosch University, 2011. / ENGLISH ABSTRACT: As the world-wide consumption of electricity continually increases, more and more pressure is put on the capabilities of power generating systems to maintain their levels of power provision. The electricity utility companies operating these power systems are faced with numerous challenges with respect to ensuring reliable electricity supply at cost-e ective rates. One of these challenges concerns the planned preventative maintenance of a utility's power generating units. The generator maintenance scheduling (GMS) problem refers to the problem of nding a schedule for the planned maintenance outages of generating units in a power system (i.e. determining a list of dates corresponding to the times when every unit is to be shut down so as to undergo maintenance). This is typically a large combinatorial optimisation problem, subjected to a number of power system constraints, and is usually difficult to solve. A mixed-integer programming model is presented for the GMS problem, incorporating constraints on maintenance windows, the meeting of load demand together with a safety margin, the availability of maintenance crew and general exclusion constraints. The GMS problem is modelled by adopting a reliability optimality criterion, the goal of which is to level the reserve capacity. Three objective functions are presented which may achieve this reliability goal; these objective functions are respectively quadratic, nonlinear and linear in nature. Three GMS benchmark test systems (of which one is newly created) are modelled accordingly, but prove to be too time consuming to solve exactly by means of an o -the-shelf software package. Therefore, a metaheuristic solution approach (a simulated annealing (SA) algorithm) is used to solve the GMS problem approximately. A new ejection chain neighbourhood move operator in the context of GMS is introduced into the SA algorithm, along with a local search heuristic addition to the algorithm, which results in hybridisations of the SA algorithm. Extensive experiments are performed on di erent cooling schedules within the SA algorithm, on the classical and ejection chain neighbourhood move operators, and on the modi cations to the SA algorithm by the introduction of the local search heuristic. Conclusions are drawn with respect to the e ectiveness of each variation on the SA algorithm. The best solutions obtained during the experiments for each benchmark test case are reported. It is found that the SA algorithm, with ejection chain neighbourhood move operator and a local search heuristic hybridisation, achieves very good solutions to all instances of the GMS problem. The hybridised simulated annealing algorithm is implemented in a computerised decision support system (DSS), which is capable of solving any GMS problem instance conforming to the general formulation described above. The DSS is found to determine good maintenance schedules when utilised to solve a realistic case study within the context of the South African power system. A best schedule attaining an objective function value within 6% of a theoretical lowerbound, is thus produced. / AFRIKAANSE OPSOMMING: Met die wêreldwye elektrisiteitsverbruik wat voortdurend aan die toeneem is, word daar al hoe meer druk geplaas op die vermoë van kragstelsels om aan kragvoorsieningsaanvraag te voldoen. Nutsmaatskappye wat elektrisiteit opwek, word deur talle uitdagings met betrekking tot betroubare elektrisiteitsverskaffing teen koste-e ektiewe tariewe in die gesig gestaar. Een van hierdie uitdagings het te make met die beplande, voorkomende instandhouding van 'n nutsmaatskappy se kragopwekkingseenhede. Die generator-instandhoudingskeduleringsprobleem (GISP) verwys na die probleem waarin 'n skedule vir die beplande instandhouding van kragopwekkingseenhede binne 'n kragstelsel gevind moet word ('n lys van datums moet tipies gevind word wat ooreenstem met die tye wanneer elke kragopwekkingseenheid afgeskakel moet word om instandhoudingswerk te ondergaan). Hierdie probleem is tipies 'n groot kombinatoriese optimeringsprobleem, onderworpe aan 'n aantal beperkings van die kragstelsel, en is gewoonlik moeilik om op te los. 'n Gemengde, heeltallige programmeringsmodel vir die GISP word geformuleer. Die beperkings waaruit die formulering bestaan, sluit in: venstertydperke vir instandhouding, bevrediging van die vraag na elektrisiteit tesame met 'n veiligheidsgrens, die beskikbaarheid van instandhoudingspersoneel en algemene uitsluitingsbeperkings. Die GISP-model neem as optimaliteitskriterium betroubaarheid en het ten doel om die reserwekrag wat gedurende elke tydperk beskikbaar is, gelyk te maak. Drie doelfunksies word gebruik om laasgenoemde doel te bereik (naamlik doelfunksies wat onderskeidelik kwadraties, nie-lineêr en lineêr van aard is). Drie GISP-maatstaftoetsstelsels (waarvan een nuut geskep is) is dienooreenkomstig gemodelleer, maar dit blyk uit die oplossingstye dat daar onprakties lank gewag sal moet word om eksakte oplossings deur middel van kommersiële programmatuur vir hierdie stelsels te kry. Gevolglik word 'n metaheuristiese oplossingsbenadering ('n gesimuleerde temperingsalgoritme (GTA)) gevolg om die GISP benaderd op te los. 'n Nuwe uitwerpingsketting-skuifoperator word in die konteks van GISP in die GTA gebruik. Verder word 'n lokale soekheuristiek met die GTA vermeng om 'n basteralgoritme te vorm. Uitgebreide eksperimente word uitgevoer op verskeie afkoelskedules binne die GTA, op die klassieke en uitwerpingsketting-skuifoperators en op die verbasterings van die GTA meegebring deur die lokale soekheuristiek. Gevolgtrekkings word oor elke variasie van die GTA se e ektiwiteit gemaak. Die beste oplossings vir elke toetsstelsel wat gedurende die eksperimente verkry is, word gerapporteer. Daar word bevind dat die GTA met uitwerpingsketting-skuifoperator en lokale soekheuristiek-verbastering baie goeie oplossings vir die GISP lewer. Die verbasterde GTA word in 'n gerekenariseerde besluitsteunstelsel (BSS) geïmplementeer wat 'n gebruiker in staat stel om enige GISP van die vorm soos in die wiskundige programmeringsmodel hierbo beskryf, op te los. Daar word bevind dat die BSS goeie skedules lewer wanneer dit gebruik word om 'n realistiese gevallestudie binne die konteks van die Suid-Afrikaanse kragstelsel, op te los. 'n Beste skedule met 'n doelfunksiewaarde wat binne 6% vanaf 'n teoretiese ondergrens is, word ondermeer bepaal.

For many years 2D machine vision has been used to perform automated inspection and measuring in the manufacturing environment. A strong drive to automate manufacturing has meant improvements in robotics and sensor technologies. So has machine vision seen a steady movement away from 2D and towards 3D. It is necessary to research and develop software that can use these new 3D sensing equipment in novel and useful ways. One task that is particularly useful, for a variety of situations is object recognition. It was hypothesised that it should be possible to train artificial neural networks to recognise 3D objects. For this purpose a 3D laser scanner was developed. This scanner and its software was developed and tested first in a virtual environment and what was learned there was then used to implemented an actual scanner. This scanner served the purpose of verifying what was done in the virtual environment. Neural networks of different sized were trained to establish whether they are a feasible classifier for the task of object recognition. Testing showed that, with the correct preprocessing, it is possible to perform 3D object recognition on simple geometric shapes by means of artificial neural networks.

M.Sc. (Computer Science) / The automation of manufacturing systems is a very important research area. This study is concerned with information infrastructures for manufacturing enterprises and the various methods that could be utilised to do enterprise modelling. The objectives of this study is to: • analyse the various enterprise modelling architectures • apply one of the architectures to a manufacturing enterprise and to evaluate this architecture • compare the various architectures.

Information technology in mature organisations is viewed as an enabler of teams working together in the product development process. Technology is no longer pursued as an end in itself, but for its contribution to cost control, product quality, and most importantly, time to profit. The focus of this research is the analysis of methodologies used to implement the Teamcenter Engineering Product Data Management (PDM) system at Delta Motor Corporation, which manages all of Delta’s CAD data. The main problem of this research is as follows: How can Delta Motor Corporation successfully implement the “Teamcentre Engineering” Product Data Management System? The main problem will be broken down into three distinct parts, namely the developing of a best practice process, analysing Delta’s implementation and making recommendations for improvement. The literature survey provides the basis for developing a best-practice process, which serves as a benchmark against which to evaluate the methodology used by Delta. Interviews were conducted with selected personnel who were involved in the implementation, and Tesch’s model for content analysis used to analyse the responses. The implementation process of Teamcenter Engineering at Delta was conducted in three phases and only the first was completed at the time of writing this research paper. For this reason, analysis revolves around the first phase of implementation, which was limited to the drawing office, while recommendations are made for the implementation of phase two and three, which roll-out this system to the rest of Delta and it’s supplier base.

M.Comm. / The concept is not new, but there are certain factors that complicated the application of this concept in actual practise: The rapid advances in technology, engineering and business processes, have left today's enterprise with a multitude of different computer applications to choose from. This puzzle consists of many variables, including : hardware, application software, operating systems, data bases and networks. An indication of the complexity of offerings available in the market today is reflected by a survey conducted by Paras on Process MRP Systems (Paras, 1992:7-28). The research problem is therefore to investigate the extent of usage of Enterprise Resource Planning (ERP) Systems in South Africa. The research project has the following objectives: To determine the extent of Enterprise Resource Planning (ERP) System usage in South African Industrial companies. To determine the different functional areas that ERP functionality is applied to in these companies, as well as trends in this area. To determine levels of support currently available to the South African Enterprise Resource Planning (ERP) System user. To determine the benefits realised . out of implementing Enterprise Resource Planning (ERP) functionality. This research explores the extent to which Enterprise Resource Planning (ERP) functionality are being used in South Africa. As these systems are mainly used in Industrial companies, this research is limited to Industrial companies within South Africa. Companies in both the discrete and process environments are included in the study. Due to the cost of implementing such systems, these companies tend to be companieswith more than 100 employees, although relevant companies with fewer employees have been included. The larger majority of the companies operate in a distributed environment, with sites spread throughout South Africa, and in neighbouring and overseas countries. Due to the exploratory nature of the research problem, and the limited full enterprise wide use of Enterprise Resource Planning (ERP) Systems in South Africa, the scope will be wide, with the intent of this study to gain a broad perspective of the topic.

The present research study will be dedicated to expounding an integrated event-based scheduling model, which model will, in turn, be based on an object-oriented method and a knowledge-based methodology. In order to complete the said model, the integration of vision and scheduling systems has been taken one step further, especially as far as the processing of events, data integration and interface design are concerned. Consequent upon the latter research, three knowledge-based domain schedulers will be expounded as scheduling control mechanisms. For the completion of the integrated scheduling system, scheduling strategies and methods based on general environments have been developed further. A wide knowledge base model will also be introduced. Finally, a case study based on the management and manufacturing environments of Omega Holdings Ltd will be conducted with the help of the proposed new scheduling model. The author hopes that the integrated event-based scheduling system will serve as an effective scheduling system tool for manufacturing and industrial-management environments alike. This thesis comprises three sections, the first of which provides an overview of scheduling literature, including scheduling types, methods and technologies in a manufacturing environment. The first section will also be dedicated to a discussion on current approaches to scheduling and their respective limitations, followed by the introduction of an integrated scheduling model for interactive event-based intelligent scheduling. This will be followed by a detailed function analysis of the model in question, based on its architecture. The second section holds the key to this thesis, as it will be dedicated to a discussion on knowledge-based domain schedulers for interactive scheduling, the implementation of three knowledge-based domain schedulers based on an object-oriented concept and event-based scheduling strategies. Consequent upon this discussion, the model of a wide integrated knowledge base will be developed further. Finally, an interactive event-based intelligent scheduling system will be developed for a dynamic manufacturing environment, whereupon an evaluation of the proposed scheduling tool and system will be effected. A case study undertaken in an existing holding company will then be used to illustrate how to realise interactive event-based intelligent scheduling and how to improve on the management function in a dynamic environment. The thesis will culminate in a summary of the pros and cons of the proposed system. In conclusion, an indication will be given as to possible areas for future research, such as multilayer scheduling in a distributed environment. / Prof. E.M. Ehlers

The primary aim of this dissertation is to provide a platform and format-neutral exchange mechanism for Layered Manufacturing (LM) and Telemanufacturing. The current exchange standard is the Stereolithography (STL) file format. The format is notoriously prone to error and frequently causes problems during the process-planning stage. The format exclusively uses a triangular boundary representation as a mathematical model and therefore lacks accuracy for models that exhibit curved features [Van00]. The goal of this thesis is therefore two-fold. Firstly, a short-term solution needs to be implemented as a stopgap measure, while a long-term solution is realised. The long-term solution will hopefully fill the communication gap caused by the STL format. A short-term solution needs to extend the capabilities of the STL format. This will compensate for the discrepancies and will allow the STL format to keep up with the requirements of the industry, while a more permanent solution is developed. In this thesis, a stopgap measure in the form of STL-Extended is proposed. STL-Extended or STL-E is a technique that redefines the semantic properties of redundant information in the existing STL file. This allows additional information to be embedded within a STL file and facilitates the storage of models more accurately. The main aim of STL-E is to remain backwards compatible with legacy hardware and software. Although this does not address the flaws that the format exhibits, it provides the most transparent integration possible. A long-term solution is proposed in the form of the Data Exchange Framework for Layered Manufacturing (DEF4LM or just DEF). This is not a new LM file format, but a platform that would allow any format that is used by the industry to potentially become an exchange standard between designer and bureau. In essence, the platform redefines the mathematical model (representation technique) as the common denominator between abstractions, as opposed to the computer model (file format). DEF4LM constitutes a four-layer architecture, which includes the Data Layer, Implementation Layer, System Layer and the Application Layer. The Data Layer represents the actual computer model being used and serves as the carrier medium for the model. The Implementation Layer consists of a descriptor and a properties file. These two elements are used to describe the syntax and the semantics of a specific file format. The various data structures are extracted and passed to the System Layer, which in turn, passes the extracted data structures to the Application Layer. The Application Layer includes the LM process-planning system, as well as the hardware and controlling software. A complementary study also conducted as part of this thesis, investigates the feasibility of a genetic algorithm to generate tool-paths for extrusion-based LM technology. The technique evolves unique tool-paths and is guided by a fitness function that includes elements that optimise for surface quality and material deposition. / Prof. E.M. Ehlers

Dissertation (MEng)--University of Pretoria, 2005. / Chemical Engineering / unrestricted

Through the use of rapid prototyping it is possible to move directly from a computer design to a nal physical product without human intervention. Telemanufacturing is an extension to rapid prototyping that presents a data communications based interface to rapid prototyping. Resource negotiating agents are able to provide a completely autonomous negotiation process. By integrating resource negotiating agents into a telemanufacturing environment, an opportunity for a completely automated supply chain is presented. / Prof. E.M. Ehlers

Presently there is a trend in manufacturing system design from stand-alone, automatic operations to Computer Integrated Manufacturing (CIM). The success of the integration depends largely on the performance of system control software. This document presents research in the design and implementation of a shop control system, for a CIM facility, using a new method called the three-layer integrated approach. Two basic techniques used in this research are expert systems and object-oriented programming. The CIM system at VPI is an automated manufacturing and assembly system. In designing the control system for this CIM facility, the design of products, production facilities, and overall system must be taken into account. In order to manage this complex system, a control system called the “shop controller” has been developed using C++, an object-oriented programming language. In addition, three real-time simulators for the cell controllers have been developed for testing and debugging the production rules of the expert system. The basic approach taken for the shop control system has several advantages: applied intelligence, program efficiency, reusability of code, and ease of maintenance. Moreover, this approach has a new feature—modularity, which is the result of combining expert systems and object-oriented programming. / Master of Science